Steve Mostyn, Texas Democratic Fund-Raiser, Dies at 46

AUSTIN, Tex. — Steve Mostyn, a Texas trial lawyer and one of the nation’s leading Democratic donors, who spent a fortune in a long effort to turn his reliably red home state blue, died on Wednesday at his home in Houston. He was 46.

The Harris County Institute of Forensic Sciences ruled the death a suicide resulting from a gunshot wound to the head. His wife and fellow lawyer, Amber Mostyn, said his death had come after a “sudden onset and battle with a mental health issue.”

The death jolted Texas politicians in both parties and left Democrats grieving the loss of a friend and wealthy patron who had been at the center of the party’s struggle to wrest power from Republicans. Texas Democrats have not won a statewide political office since 1994.

“Texas has lost one of its giants for justice and one of its most important voices for those without the ability or means to fight for themselves,” said Wendy Davis, a former Democratic state senator who ran for governor there in 2014, losing to Greg Abbott, a Republican and the current governor.

The Mostyns and their law firm’s political action committee helped bankroll Ms. Davis’s campaign as they donated nearly $10 million to state races during the 2014 election cycle.

The Mostyns had also been major donors at the national level. They gave nearly $3.5 million to candidates for federal office in the 2016 election, making them the 64th-largest donors in the country, according to the Center for Responsive Politics. Every cent went to Democrats.

Mr. Mostyn also gave two contributions of $1 million each to Priorities USA Action, a Democratic “super PAC” that supported Hillary Clinton’s presidential campaign in 2016, according to the center’s outreach coordinator, Brendan Quinn.

In an interview with The Texas Tribune in September, Mr. Mostyn signaled that he wanted to scale down his political activities and was encouraging others to “step up” to help support the Democratic cause.

“We’re just a little bit slowing down,” he said. “I want to go watch Friday night football with my son and go to my little girl’s swim meets,” he said. He added, “We’re at the point where you’re running, running, running, and you look up one day and you say we’re doing fine, but are we really enjoying the things we want to be enjoying?”

John Steven Mostyn was born in Perth, Australia, on March 25, 1971, the son of George and Glenda Jean Mostyn. His father was in the oil industry and his mother was an educator.

Mr. Mostyn grew up in Whitehouse, a small East Texas town near Tyler, and graduated from the University of Texas at Austin in 1994 and the South Texas College of Law in 1996.

As founder of Mostyn Law in Houston, he built a reputation as one of the state’s power lawyers by building a fortune through homeowner suits against insurance companies after hurricanes and other storms.

In addition to his wife, he is survived by a son, Mitch, 16; and a daughter, Ava, 10.

Besides their fund-raising, the Mostyns were deeply involved in the state Democratic Party’s strategic decisions on where to place resources and staff to boost Democratic turnout, particularly among Hispanics, said Gilberto Hinojosa, the state party chairman.

Craig McDonald, executive director of Texans for Public Justice, which tracks state campaign contributions, said the Mostyns had unquestionably been the top Democratic fund-raisers in Texas, although the overall amounts had declined recently.

Their contributions totaled $1.8 million in 2016, the biggest amount by a solidly Democratic donor, Mr. McDonald said, though far below the $9.8 million they gave in 2014, when Democrats were trying to reclaim the governor’s office. They gave $4.5 million in 2012.

“There is no solidly Democratic donor that has come close to the amount that the Mostyns have given over the past decade to political candidates,” Mr. McDonald said. “Does it look like someone is ready to fill the hole in political fund-raising for Democrats? We don’t see it yet.”

A version of this article appears in print on , on Page A21 of the New York edition with the headline: Steve Mostyn, 46, Texan Donor Who Bankrolled Democrats. Order Reprints | Today’s Paper | Subscribe